John Bercow says he is ready for the Speaker's role

John Bercow, a former hard-right Tory student activist, emerged as the early frontrunner to become the Speaker of the Commons when he pledged to champion reforms to Britain's "broken" parliament.

With support from more than 100 MPs, Bercow announced his intention to stand and warned that British politics was entering "deeply dangerous territory" which was boosting extremists.

In a lengthy manifesto, Bercow pledged to become a "forthright advocate for parliamentary democracy" which would see him break with tradition as Speaker by making regular appearances on television to speak up for MPs.

"We must make no mistake, parliament is broken," Bercow said. "Disengagement from politics and indifference to what we do have given way to outright public ridicule and contempt. This is not just sad, it is deeply dangerous, because it provides fertile ground on which extremists feed."

Bercow's decision to throw his hat into the ring just over 24 hours after Michael Martin announced he would stand down on 21 June showed that MPs were heading for one of the liveliest elections for Speaker in recent memory. Sir Alan Beith, a senior Liberal Democrat MP, announced on Tuesday night that he was a candidate but support for him has yet to surface.

In his manifesto, Bercow said the Speaker should do more than preside over sittings of the Commons and chair the various committees that run parliament. He would use his mandate from MPs to take a visible role in forcing through reforms and speaking up for parliament, even if that meant confronting the government.

Bercow has strong support from Labour MPs who have watched with approval as the former far-right Monday Club member has evolved since his election in 1997 from one of the Tories' main attack dogs to become an emollient and centrist figure. But he upset many Tory MPs by conducting a report for the prime minister into children with learning difficulties.

Labour whips, who have no formal role in the election, were keen to promote ­Bercow. One said: "The Tories have tried to stuff us by taking down one of ours, so we're going to stuff them by voting for someone they hate. But they can't complain; John Bercow is a Conservative MP, if only nominally."

Bercow announced his intention to stand in an exchange of letters with the Labour MP Martin Salter, who called for a "modernising and reforming candidate". In his reply Bercow made clear that he would rip up convention. "For far too long the House of Commons has been run as little more than a private club by and for gentleman amateurs," he wrote. "It remains beset by antiquated practices which would not survive for a moment in any well-run organisation in the public, private or voluntary sectors."

Bercow said that clearing up the mess over allowances was an urgent priority, but he made clear that reform would have to go much deeper. He pledged:

• Changes to the composition of Commons select committees, a hint that he would strip party whips of the right to nominate members;

• Giving backbench MPs a greater role in scutinising the government;

• To act as an "ambassador for parliament to the people".

Victory for Bercow would mark a remarkable turn for the once ardent Thatcherite who was so determined to become an MP in 1997 that he chartered a helicopter to take him to two selection meetings on the same night. He was also an adviser to the former cabinet minister Jonathan Aitken and was once secretary of the immigration and repatriation committee of the Monday Club.

Bercow, who moderated his views after marrying his Labour-supporting wife Sally Illman in 2002, said in his letter: "I have been on a political journey of enlightenment from the Thatcherite right to the political centre ground."

Senior Tories can barely bring themselves to speak to Bercow. One shadow cabinet minister said: "The problem with John Bercow is that he discovered sex and New Labour at the same time."

Bercow is bound to face a challenge because he will attract support from few Tory MPs. Sir George Young, the veteran former Tory cabinet minister, would win support from many Tories and older, centre ground Labour MPs. But he may be seen as too patrician at a moment when parliament needs reform.

Other likely candidates include the former Labour minister Frank Field, who has the opposite problem to Bercow: he would attract strong Tory support but virtually no support from Labour MPs.

David Davis, the former shadow home secretary, is loudly declaring that he has no interest but many Tories believe he is "on manoeuvres".